Disc-type recording media to which optical reading is applied (hereinafter referred to as “optical discs”), such as DVDs (Digital Versatile Disks) and CDs (Compact Discs), have rapidly become popular for applications of storing computer files and movie streams. Optical discs have a large storage capacity and random accessibility. Unlike contact-type magnetic recording media, there are no concerns regarding wear and damage on a recording surface as a result of reading, head crash, or the like. Furthermore, the disc surface is sturdy, and the risk of data being accidentally deleted is low. In recent years, optical discs have also been widely used as external recording media and external storage devices for computers.
Since disc-type recording media are randomly accessible, when an AV stream is recorded, it is possible to efficiently find a favorite scene. Furthermore, since access to data is performed in a non-contact manner, media can be used without causing them to be deteriorated.
Furthermore, in recent years, as the recording capacity of disc-type recording media has increased, video cameras of the type that store movies on a disc in place of previously used recording tape have appeared (for example, refer to Patent Document 1). For example, the number of users of DVD video cameras has increased year by year from the year 2000 and such cameras were sold due to the virtues of high image quality and high ease of use, such as editing being possible.
When the convenience of a user is considered, it is desirable in recording applications that a movie stream captured using a video camera or the like is formed as individual parts for each recording section or for each playback section so that editing, such as deletion of some parts, can be performed. On the other hand, there has been a demand that a recording medium on which recording and editing operations have been performed may be taken out as desired from a recorder, loaded into a play-only device in a house and played, and the user wants to view the captured movie on a TV monitor.
Accordingly, as a standard that is mainly targeted at applications for video cameras, in AVCHD (Advanced Video Coding High Definition), recording compatibility and additional recording compatibility functions are added to establish a specification regarding a data format for a high-definition (HD) video camera.
At this point, “deletion editing” for deleting a portion of a section of a stream recorded on a medium may be one of the following two types: nondestructive editing for deleting references from a playlist so that titles are only not seen by the user and the stream data remains on the medium; and destructive editing for actually deleting stream data recorded on a medium so as to restore the recording capacity. In the latter destructive editing, there are problems regarding a stream format. This point will be described below.
As a stream file format of AVCHD, an MPEG (Moving Picture Experts Group)-2 system has already been decided upon. According to the MPEG system specification, in order to achieve synchronization between audio and movie packets, several pieces of time stamp information are used.
In the MPEG2 system, there are two types of streams: PS (program stream) streams and TS (transport stream) streams. In AVCHD, a packet structure in which 4-byte TP_extra_header( ) is attached is used. A TS stream is formed in such a manner that video and audio data is divided into TS packets of a fixed byte length. When a stream is to be reproduced, it is input temporarily to a buffer and then decoded. As a consequence, unless the time intervals are adjusted with consideration of the status of the buffer, an overflow or an underflow is caused to occur in the buffer of a receiver, thereby obstructing the seamless nature of stream playback. For this reason, when stream data is recorded on a recording medium or is reproduced from a recording medium, suitable information on the arrival time of data for data reproduction is necessary. Therefore, a time stamp (ATS) regarding a data arrival time is inserted into all packet data transmitted in a TS format, and packet data is reproduced on the basis of the information on an arrival time.
When a stream is to be recorded, packet data received at a specific time interval is recorded on a recording medium. On the other hand, in order to reproduce recorded packet data, a counter with which packet data is transmitted to a decoder of a playback apparatus at the same time interval as the above specific time interval is necessary. Such a counter is called an arrival time clock (ATC) counter, and the counter value thereof is inserted into the packet data. When the recorded packet data is to be reproduced, the time interval at which packet data should be transmitted to a buffer of the decoder is determined on the basis of the counter value contained in the packet data. On the basis of the counter value generated by the ATC counter, an ATS is attached to packet data, and the packet data is output on the basis of the ATS when data is to be reproduced. In the AVCHD standard, it is stipulated that a single ATC is provided in one stream file, and the ATS is continuously increased monotonically.
The description returns to the editing of deleting a stream. When a section in which deletion editing is to be performed by destructive editing is an intermediate portion of a stream, the ATS possessed by the packet data at the end of the first half of the remaining stream and the ATS possessed by the packet data at the beginning of the second half thereof are non-continuous. Therefore, it becomes not possible to maintain having only a single ATC in the stream file.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2004-120364